Last night when I went to bed and my girls were playing, I heard more racket than normal (almost like trying to get grasp/loosing grasp of the bars of the cage), and then what sounded like whimpering, almost like a puppy does when he's seemingly sad or hurt.
I was in that 'half asleep' stage, so it took a moment, but I turned my lamp on and went to their cage (they're in my room). One of the hanging toys was 'rocking' back and forth, and both girls were on the 'floor' of the cage, next to each other.
They looked at me like 'what!?' and then started running around again, like nothing happened.

Now, my girls aren't always side by side, as much as they love each other, and when I turned my light on they were right next to each other, like one was checking on the other.

So what was this sound? Was it a 'hey I'm hurt a lil bit' deal or something...?

They're still very active and eating and drinking, so I'm sure they're fine, but that was a sound I had never heard before (granted, I haven't had them that long) and it kind of freaked me out.

It was probably just them talking to each other. My guys make sooo many different sounds in the middle of the night it sounds like I have a full jungle in my bedroom.
I wouldnt be too worried :)

I was scared she was hurt. It literally sounded like she fell after trying to catch her grip, and then whimpering, like a hurt or sad puppy. I go so scared. It took seeing them both running around normally that they were ok (being that it was dark, I don't know who got hurt).

I can't get over the wide range of sounds they make. Like I said, they're in my room (they wake me up about once per night) so I hear a lot of their activities. I'd just never heard THAT noise, and it following all of that commotion worried me.

it could have been them just barking... mine do that alot.. hearing all 3 bark is so cute and it sounds like a tiny dog :)

My female is in a different cage than my boys so when the girl wants the boys to come out of the pouches she barks. i'm guessing its jus something they do.

Oh no. This was most certainly NOT barking. It was a whimpering sound. They bark for me almost every single morning, so I definitely know they're barking.
This was a new sound to me; I've never heard it before last night. Like I said, it sounded just like a dog whimpering/whining.

Hmm i dunno then i havent heard it. i hear what sounds like crickets lol when it sounds like them arguinhg.. and barking and crabbing and when my female was pregnant i heard her singing

omg singing gliders. THAT would be neat to hear. I haven't heard the whimpering sounds since the other night, but today while in their pouch, which I had rolled down and in my bra all day, they would go through bouts of clicking/chattering while looking up at me. My heart kept melting.

Singing is not pleasant at all. I have no clue why someone named it that. It almost sounds like a rattlesnake rattle to me. What it is, is mom trying to shake a joey loose from her nipple because she's uncomfortable. When you see it, it's even more bizarre. She looks like she's twitching/vibrating. It isn't cute at all.

Oh. Shoot. SINGING sounds neat. What you're describing.. not so much.

the rattle snake sound is not the singing... they sing to their babies, i wish i could describe it but i cant. but each mama has a different sound when singing to her joeys

You can look it up on youtube. jus put in gliders singing or glider noises and you can hear them singing.